One example of power semiconductor modules is provided with a multilayer substrate having an insulating plate and a circuit plate, a semiconductor chip having a front surface having an electrode and a back surface fixed to the circuit plate, and a connection terminal. The multilayer substrate has an integrated structure configured by the circuit plate disposed on the front surface of the insulating plate and a metal plate disposed on the back surface thereof. Raw materials of the circuit plate and metal plate are generally copper and aluminum. The semiconductor chip is bonded to the circuit plate by solder. The connection terminal may be bonded to the circuit plate by solder. Further, a heat sink may also be bonded to the metal plate by solder.
For assembling the power semiconductor module, solder is disposed at a position for bonding the semiconductor chip on the circuit plate of the multilayer substrate, and then, the semiconductor chip is disposed on the solder, followed by heating and melting the solder for bonding. The situation is the same for bonding the connection terminal to the circuit plate by solder. Further, the metal plate of the multilayer substrate and the heat sink are bonded to each other by solder which is disposed therebetween and then molten by heating.
The surfaces of the circuit plate and the metal plate of the multilayer substrate may be covered, before solder-bonding, with a rust preventive for prevention from oxidation and corrosion. Benzotriazole-based rust preventives are generally used as such rust preventives (Patent document 1).